package com.lingfeng.rpc.util;


import cn.hutool.core.util.RandomUtil;

import java.util.concurrent.locks.ReentrantLock;

/**
 * @author: wz
 * @Date: 2019/10/31 13:58
 * @Description:
 */
public class SnowFlake {

    /**
     * 起始的时间戳
     */
    private final static long START_STMP = 1480166465631L;

    /**
     * 每一部分占用的位数
     */
    private final static long SEQUENCE_BIT = 12; //序列号占用的位数
    private final static long MACHINE_BIT = 5;   //机器标识占用的位数
    private final static long DATACENTER_BIT = 5;//数据中心占用的位数

    /**
     * 每一部分的最大值
     */
    private final static long MAX_DATACENTER_NUM = ~(-1L << DATACENTER_BIT);
    private final static long MAX_MACHINE_NUM = ~(-1L << MACHINE_BIT);
    private final static long MAX_SEQUENCE = -1L ^ (-1L << SEQUENCE_BIT);

    /**
     * 每一部分向左的位移
     */
    private final static long MACHINE_LEFT = SEQUENCE_BIT;
    private final static long DATACENTER_LEFT = SEQUENCE_BIT + MACHINE_BIT;
    private final static long TIMESTMP_LEFT = DATACENTER_LEFT + DATACENTER_BIT;

    private long datacenterId;  //数据中心
    private long machineId;     //机器标识
    private long sequence = 0L; //序列号
    private long lastStmp = -1L;//上一次时间戳
    private final static ReentrantLock UUID_LOCK = new ReentrantLock();

    public SnowFlake(long datacenterId, long machineId) {
        if (datacenterId > MAX_DATACENTER_NUM || datacenterId < 0) {
            throw new IllegalArgumentException("datacenterId can't be greater than MAX_DATACENTER_NUM or less than 0");
        }
        if (machineId > MAX_MACHINE_NUM || machineId < 0) {
            throw new IllegalArgumentException("machineId can't be greater than MAX_MACHINE_NUM or less than 0");
        }
        this.datacenterId = datacenterId;
        this.machineId = machineId;
    }

    public static Long next() {
        return instance().nextId();
    }

    public static SnowFlake instance() {
        return initSnowFlake.snowFlake;
    }

    //单例模式
    final static class initSnowFlake {
        //随机生成的机器码
        static final long dataCenterId = RandomUtil.randomLong(0, 30);
        static final long machineId = RandomUtil.randomLong(0, 30);
        public static final SnowFlake snowFlake = new SnowFlake(dataCenterId, machineId);
    }


    /**
     * 产生下一个ID
     *
     * @return
     */
    public long nextId() {
        try {
            UUID_LOCK.lock();
            long currStmp = getNewstmp();
            if (currStmp < lastStmp) {
                throw new RuntimeException("Clock moved backwards.  Refusing to generate id");
            }
            if (currStmp == lastStmp) {
                //相同毫秒内，序列号自增
                sequence = (sequence + 1) & MAX_SEQUENCE;
                //同一毫秒的序列数已经达到最大
                if (sequence == 0L) {
                    currStmp = getNextMill();
                }
            } else {
                //不同毫秒内，序列号置为0
                sequence = 0L;
            }
            lastStmp = currStmp;
            return (currStmp - START_STMP) << TIMESTMP_LEFT //时间戳部分
                    | datacenterId << DATACENTER_LEFT       //数据中心部分
                    | machineId << MACHINE_LEFT             //机器标识部分
                    | sequence;                             //序列号部分
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            UUID_LOCK.unlock();
        }
        return 0L;
    }

    private long getNextMill() {
        long mill = getNewstmp();
        while (mill <= lastStmp) {
            mill = getNewstmp();
        }
        return mill;
    }

    private long getNewstmp() {
        return SystemClock.now();
    }
}
